This invention relates to polymeric powders suitable as electrostatographic toner and carrier particles and to a method of preparing the same. More particularly, this invention relates to a method of preparing toner and/or carrier particles having controlled and predetermined size and size distribution.
Commonly, polymeric particles including toner and carrier are prepared by numerous methods, probably the most primitive of which is by grinding bulk polymer materials to a suitable particle size and/or particle size distribution. The disadvantages of this process are widely known. First, the particles are of a totally irregular shape after grinding and may not be suitable for the intended purpose and secondly, because of the toughness of some types of polymeric materials grinding cannot be accomplished.
U.S. Pat. No. 3,586,654 discloses numerous techniques for preparing polymer powders in addition to the grinding technique including a solution process, wherein a polymer is dissolved in a solvent and then precipitated from the solvent by the addition of a non-solvent that is miscible with the solvent; the dispersion process wherein molten polymer is introduced into a water solution containing dispersing agents such as soaps, and several similar techniques including the claimed invention thereof which is a process for preparing powders by dispersing polymer particles in a liquid that is a non-solvent for the polymer, heating the dispersion together with agitation above the melting temperature of the polymer and then cooling to recover the solidified polymer particles. While these techniques are useful under certain specified conditions they all suffer from disadvantages either in processing conditions, such as, the need for pressure vessels should the melting temperature of the polymer particles be greater than the boiling point of water or other non-solvent used; or in the condition of the particles at the end of the technique, such as coated with the surfactant and the like. Such conditions render particles impractical for use in many applications, particularly in their use in electrostatography wherein the particles are triboelectrically charged in order to achieve the intended result.
U.S. Pat. No. 3,847,886 teaches a method of making small particles of solid polymer by dissolving a polymer in a water immiscible polar solvent, emulsifying the solution in water, generally with the use of an emulsifying agent, adding a water immiscible organic liquid that is miscible with the solvent but a non-solvent for the polymer and recovering the polymer particles.
U.S. Pat. No. 4,254,207 provides a method of making small spherical particles of crystalline condensation-type polymers by agitating a fluid mixture of the crystalline polymer in an aprotic liquid which is a non-solvent for the polymer and containing an acid-modified polymer of propylene at a temperature above the crystalline melting point of the polymer, cooling and recovering the solid particles from the aprotic liquid. These last two methods suffer the disadvantages that they are limited with regard to the type of polymer that can be employed to make the powder particles or the condition of the powder that results because of the various ingredients that are employed in the process.
Japanese Kokai NoSho 61-91666 discloses a method of making toner by dispersing a binder resin in an halogenated hydrocarbon solvent, dispersing the mixed solution in an aqueous medium and after removing the solvent, dehydrating and drying the resulting particles
Polymeric powders can also be prepared by emulsion and suspension polymerization techniques. In suspension polymerization, monomer droplets are dispersed in a water solution and polymerization takes place within each droplet. The solidified polymer particles are separated from the remainder of the system. Patents utilizing these techniques referred to as "limited coalescence" include U.S. Pat. Nos. 2,934,530, 3,615,972, 2,932,629 and 4,314,932. These methods, however, are limited with respect to the type of polymer that can be prepared.